The first, at Oak Hill Middle School, wasexactly one weekafter the Boston Marathonbombings.

The second happened the next day, at Oak Hill High School.

The latest wasThursday afternoon, at the Carrie Ricker Elementary School.

According to RSU Superintendent Jim Hodkin, all three threats were written in school bathrooms.

"Kids are frustrated with it, and they feel unsafe," said Superintendent Hodkin.

He added thatthree weeks ago, just before April vacation, there had been another bomb threat within the school district.

"These things go in cycles, and rarely ever is it one incident and then it's done," said Hodkin.

Hesaid the district has been following evacuation plans put in place, and working with local lawenforcement to apprehend the suspects.

It hasgiven him the chance to re-examineevacuation procedures. He explained that when a threat comes in to the middle school, students areevacuated to the high school, and viceversa.

Someone mentioned to him that if someone wanted to harm students, they would simply threaten one school, and target the evacuation destination.

"Schools should go through the process of reviewing their response plans on a regular basis, particularly, unfortunately, in the world we live in now," said Hodkin.

He said the threats are being treated as criminal investigations, and with the help of local law enforcement, they have identified their suspect in the middle school bombing threat as a student from that school.